how do fertilizer values work?


Can someone explain NPK numbers in soluble fertilizer to me?

Would one cup of 10-10-10 all purpose fertilizer equal two cups of 5-5-5 all purpose fertilizer?

I mean is it that simple?

What is in the rest of the fertilizer if only 15 or 30% is NPK?

In: 2

It is that simple, at least if you are actually using scales to measure your fertilizer and not a cup. The fertilizer values are by weight and not volume. The rest of the fertilizer that is not Nitrogen, Potassium or Calcium is not specified. However the compounds that is used as a reference is quite expensive and potentially unstable. So instead manufacturers will use chemicals which is widely available and can be mined or farmed. This is usually the source of any inert compound.

For example the 10-10-10 fertilizer may be made from ground up animal bones. These are cheap as slaughter houses produce them as byproducts. But it does have other compounds in them. Most of them are also beneficial to your plants. For example Iron and Magnesium. But a large part is organic compounds, some of it will be used by the bacteria and insects in the soil which helps the plant out but in general it just rots away.

Hi friend. Try not to think in terms of these cups, it goes by weight (like most things should lol) so it’s percent by weight. If you want 1 pound of N, then you need 10lb of a 10-X-Y to get your 1lb (because 10% of 10lb is 1lb). unless you’re using the entire contents of some given container (eg 25lb of lawn fert across entire lawn) then it really is best to weigh out the fert or at least get an idea of the density and write it down for use to determine these volumetric measurements (but I don’t advise this)

The rest of the stuff is mostly fillers which could be for form and ease of dispersing the active or just sort of an inherent consequence of the nature of the given product